A wind turbine known in the art comprises a tapered wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with a number of wind turbine blades is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on FIG. 1.
In order for a specific fluid in a closed fluid circulating system to function properly, there has to be a certain amount of the fluid in the system. Monitoring fluid levels in mechanical systems such as the cooling fluid level in cooling systems or the oil level in hydraulic and lubrication systems is therefore a very well known method of monitoring the fluids functionality.
For instance is it well known to monitor the oil level in the oil sump of a wind turbine gearbox by means of a floater, which triggers an electrical contact, when the floater position is above or below a certain level.
Gears churning through the sump, vibrations and other factors stirring up the oil, makes it necessary to filter out short-term fluctuations of the oil level. This is normally done by installing the floater in bypass vessels, where the fluid level communicates with the reservoir through nozzles, which, because of the relative small holes in these nozzles, dampens the fluctuations.
But the viscosity of the oil increases when its temperature drops, and if the oil becomes too thick, the communications between the oil levels in the reservoir and the vessels is interrupted or the measurements becomes so defective that the measurements are useless.
Furthermore, the factors stirring up the oil also can enable that a large amount of air is entrained in the oil, making the floater heavier that the oil and thereby submerging it, or simply enlarging the oils volume. Both scenarios produce mal-readings, which in worst case could lead to a breakdown of the gearbox.
An object of the invention is therefore to provide for a technique for monitoring the fluids functionality in a closed fluid circulating system with a reservoir.
Especially it is an object of the invention to provide a reliable and cost-efficient technique for monitoring the fluids functionality in a closed fluid circulating system with a reservoir in a wind turbine.